Quantitative permeability changes and the role of lung histamine in the alveolar capillary membrane leak syndrome associated with such conditions as endotoxin injection, hemorrhagic hypotension, and ethchlorvynol injection have not been fully detailed. Employing the in vivo filled dog lung model and the right lymphatic duct cannulation model, we will (1) characterize the normal alveolar epithelial and pulmonary microvascular permeability to graded narrow ranged dextrans (mol. rad. varying from 10 to 80 A) and albumin. Normal lung liquid histamine levels will be determined. (2) Following endotoxin, ethchlorvynol injection and acute hemorrhagic hypotension determine the changes in permeability for these graded sized dextrans compared to normal. Histamine levels in the lung and blood will be measured before and after the various insults. (3) We will attempt to block any histamine effect with H1 and H2 receptor blockers prior to the various insults and determine alveolar epithelial and pulmonary microvascular permeability changes.